Braw day, complicated situation…
11th February 2024
Today was unexpectedly bright and sunny for the most part, although the clouds did appear later. Despite some very light snowfall overnight it was also dry despite the forecast of snow showers.
In any case, this gave a good opportunity to see high up around the ‘Post Face’ and the top of ‘Raeburn’s Gully’. SAIS Lochaber contributed an excellent post yesterday describing the awkwardness of forecasting in an Easterly. Well worth a read the complex terrain of Coire Ardair is not without challenges also, particularly under the current airflow.
Due to the turbulence in the coire cross-loading of windslab on crag aprons and in gullies has occurred. This has often been localised, and in wind sheltered locations mid way up the cliffs, rather than at the top in mutli aspect gully exits where it may normally be found. Localised in nature, means that there are pockets of this sensitive windslab immediately next to firm older snow which is very stable. With good visibility these localised pockets (sometimes described as pillows in the case of small drifts) can be seen and avoided by sticking to the older scoured snow.
“See and avoid” is a good travel strategy but relies on good visibility (and experience). This is where things might get tricky in to the next couple of days as new snow is expected. A blanket of soft fresh snow will cover the existing localised deposits disguising their presence. So while the hazard level will remain the same, using the forecast and moving around in the mountains will become more difficult. Careful route choice will be required.
(Above) An image from Friday 9th February compared with today the 11th February. Notice the fresh snow and ice development.
Looking into Coire a’Chriochairein (aka the stone coire). Note the localised snow accumulation. Cross loading is noticeable along the ridge line in the top left of the image, with scoured ground to the left of the prominent snow arete (centre left).
Looking into ‘The Window’.
As the day progressed the windspeed increased and redistribution of snow became increasingly evident. Notice the wisps of spindrift along the plateau edge and scarp slopes below.
My route today took me into the seldom visited Coire nan Gamhna. Quite a unique spot with an almost totally symmetrical shape. But there is one other thing that makes it quite special and that is the geology. One side is Psammite of the Loch Laggan Formation, while the other is Semipelite of the Ardair Semipelite Formation. Both are 1000 – 541 million years old. I could barely contain my excitement when I found this rock lying on the snow with a clear boundary between the two!
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Colin
11th February 2024 7:03 pm
That’s a great sample. Quite a find!